Bradford assay

What is biophotonics?

Biophotonics describes the technology that focuses on the interaction of biological materials with light and other forms of radiant energy.

What is the quantum unit of radiant energy?

The photon.

What are the ways light can interact with biomolecules?

Reflection, absorption, transmission, and light scattering.

What does the Bradford assay measure?

The absorption of light as a function of wavelength to determine protein concentration.

At what wavelength does the Bradford assay peak absorbance occur?

595 nm.

What color does the protein-dye complex turn in the Bradford assay?

Blue.

What is the role of the spectrophotometer in the Bradford assay?

It measures the absorbance of light at specific wavelengths to quantify protein concentration.

What are the three colorimetric methods for determining total protein content mentioned?

Biuret, Lowry, and Bradford assays.

Which protein assay is the oldest and least sensitive?

The biuret assay.

What is the main disadvantage of the Lowry method?

It is affected by interference from many common laboratory reagents and chemicals.

What dye is used in the Bradford protein assay?

Coomassie Brilliant Blue G-250.

What happens to Coomassie G-250 dye when it binds to proteins?

It converts to a stable unprotonated blue form, shifting its absorption maximum from 470 nm to 595 nm.

What is the relationship between the intensity of blue color and protein concentration in the Bradford assay?

The more protein present, the more intense the blue color.

What are the four main steps of performing the Bradford assay?

1. Prepare dilution series of known protein standards and unknowns. 2. Add Bradford dye and incubate. 3. Bind dye to protein and read absorption at A595. 4. Compile data into a standard curve for protein concentration determination.

What is casein?

The most abundant form of protein in milk.

How many amino acids are in casein?

224 amino acids.

What is the molecular mass of casein?

24,967 daltons.

Which amino acids in casein strongly react with Coomassie dye?

4 arginines, 1 tryptophan, 4 tyrosines, and 4 histidines.

What is the significance of the wavelength 470 nm in the Bradford assay?

It is the peak absorption wavelength of the cationic form of Coomassie G-250 dye.

What type of interactions does Coomassie G-250 dye have with proteins?

Electrostatic interactions, electron stacking interactions, and weak interactions with polar amino acids.

What is the purpose of creating a standard curve in the Bradford assay?

To estimate the quantity of protein in an unknown sample based on the intensity of blue color.

What is the maximum absorbance wavelength of the unprotonated blue form of Coomassie G-250?

595 nm.

What is the role of the cationic form of Coomassie G-250 in the Bradford assay?

It binds to proteins and changes color upon binding.

What is the incubation time recommended for the Bradford assay?

More than 5 minutes but not exceeding 60 minutes.

How does the Bradford assay benefit from its simplicity?

It allows for easy performance and is highly sensitive to protein concentrations.

What is the principle behind the Bradford assay?

The binding or coating of proteins by Coomassie dye molecules.

What is the molecular weight of Coomassie dye?

854 daltons.

What is the average molecular weight of an amino acid?

110 daltons.

What does a high R² value indicate in a standard curve?

A strong linearity of the data and a better estimate of concentration.

What R² value reflects a high degree of linearity?

Correlation coefficients greater than 0.9.

What materials are needed for the Bradford assay?

1x Bradford dye reagent, microtubes with protein standards, test milk samples, unknown samples, PBS, micropipets, cuvettes, and parafilm.

What is the first step in preparing milk samples for the Bradford assay?

Prepare a 1:50 dilution of the milk samples using 1x PBS.

How long should the samples incubate after adding the dye reagent?

At room temperature for at least 5 minutes but not exceeding 60 minutes.

How do you qualitatively determine the concentration of unknown samples?

By visually comparing the color of unknown samples against the standards.

What should be done to the cuvettes after adding the dye reagent?

Cover each cuvette with parafilm and invert to mix.

What is the significance of the absorbance data in the Bradford assay?

It is used to plot the standard curve for estimating unknown protein concentrations.

What is the Bradford Assay classified as?

A colorimetric assay.

What should be done with the cuvette labeled 'blank'?

Add 20 µL of 1x PBS to it.

What is the purpose of using a dilution series in the Bradford assay?

To create a range of known concentrations for comparison with unknown samples.

What does the term 'unknown samples' refer to in the context of the Bradford assay?

Samples with unknown protein concentrations that need to be analyzed.

What is the expected outcome of comparing unknown samples to standards?

To estimate the protein concentration of the unknown samples.

What is the function of the DeNovix spectrophotometer in the lab?

To automatically compare samples to the standard curve and determine concentration.

What is the first step when preparing the DeNovix for quantitation?

Turn on the DeNovix and enter the required information.

What is the purpose of labeling microtubes in the lab exercise?

To identify different samples and standards during the experiment.

What is the significance of using fresh pipet tips for each sample?

To avoid cross-contamination between samples.

What is the role of the absorbance data in creating the standard curve?

It is plotted against known protein concentrations to establish a reference for unknowns.

What is the expected result after incubating the cuvettes?

A color change indicating the presence of protein, which can be compared to standards.

What should be recorded in Table 1 during the lab?

The estimated protein concentrations for the unknown samples.

What type of assay is being set up in the window?

Bradford assay

What needs to be changed in the assay setup?

Change from BCA to Bradford

What is the cuvette window spacing set to?

10 mm

What is the purpose of entering known standard concentrations in the Bradford assay?

To check prepared standards and calculate unknown concentrations

What button do you press to enter the known standards?

Enter standards button

What is the first standard concentration to enter?

0.125 mg/mL

How many times should each standard be run?

5 times

What does the R-square value indicate in a standard curve?

The goodness of fit of the model

What is the formula used to calculate the required volumes for each standard?

C₁V₁=C₂V₂

What is the concentration of the stock solution used for preparing standards?

2.0 mg/mL

What is the blank in the standard set for the Bradford assay?

PBS (Phosphate Buffered Saline)

What is the significance of the R² value being 1?

All variation in y values is accounted for by x values

What does an R² value of 0 indicate?

None of the variation in y values is accounted for by x values

What is the dependent variable in the context of the Bradford assay?

Standard set of concentrations (y)

What is the independent variable in the context of the Bradford assay?

OD readings (x)

What should you NOT do when collecting unknown sample data?

Do not reblank the instrument

What happens if the samples are not labeled correctly?

You will not know which concentration corresponds to each sample

What is the dilution factor that needs to be added to the sample concentration?

The dilution factor from any sample dilution (e.g., 50/50 dilution)

What is the purpose of the standard curve in the Bradford assay?

To determine the concentration of unknown samples based on known standards

What is indicated by a low R² value in pipetting skills?

More variability in pipetting, leading to inaccurate readings

What is the first calculation example provided for standard preparation?

V₁ = (1.5 mg/mL)(50 µL) / 2.0 mg/mL = 37.5 µL of 2.0 mg/mL Standard

What is the amount of PBS needed when preparing a standard of 1.5 mg/mL?

12.5 µL PBS

What should be checked if there is a discrepancy with a low R² value?

Check controls, instrument issues, or the MedTech's skills

What does the term 'standard curve' refer to in the Bradford assay?

A graph plotting known concentrations against their corresponding OD readings

What is the importance of accurate pipetting in biological research?

Small mistakes can lead to larger issues in research outcomes